Sagittal Band Rupture Location
Sagittal band rupture occurs predominantly on the radial side of the finger, with the radial sagittal band being the critical structure that prevents ulnar subluxation of the extensor tendon at the metacarpophalangeal joint. 1
Anatomic Basis for Radial-Sided Rupture
The radial sagittal band is the primary stabilizer against ulnar tendon subluxation, and its disruption—either partial or complete—is responsible for the characteristic ulnar displacement of the extensor tendon seen clinically. 2
Biomechanical cadaveric studies demonstrate that serial sectioning of the ulnar sagittal band produces no extensor tendon instability, whereas partial proximal sectioning of the radial sagittal band alone can produce tendon subluxation, and complete radial sagittal band sectioning produces frank tendon dislocation. 2
The majority of traumatic cases involve disruption of the radial sagittal band with consequent ulnar subluxation of the extensor tendon, particularly in patients without rheumatoid arthritis. 3
Clinical Presentation Pattern
The long (middle) finger is most commonly affected by extensor tendon instability following sagittal band disruption, while the small finger is least commonly affected. 2
Even partial division of the radial sagittal band can result in tendon dislocation in the middle and ring fingers, which explains why conservative treatment with extension splinting may be feasible for acute injuries in these digits. 4
In the little finger specifically, complete section of the sagittal bands caused ulnar dislocation in only one out of seven cadaveric hands, indicating anatomic variation in susceptibility. 4
Mechanism of Injury
Greatest forces are inflicted on the sagittal band when the MCP joint is in full extension or less frequently in full flexion, representing the likely mechanism of injury. 2
Wrist flexion significantly contributes to extensor tendon instability after sagittal band disruption and may exacerbate the severity of injury, with proximal rather than distal sagittal band compromise being the primary contributor to tendon instability. 2
Injury typically results from a direct blow to the hand or relatively low-energy mechanisms, with associated injuries including collateral ligament sprains, capsular injury, and osteochondral fractures. 1
Imaging Considerations
- MRI is ideal for evaluating tendon injuries and surgical planning in the hand, though specific guidelines for sagittal band imaging are not well-established in major radiology guidelines. 5